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6BBL tuning with proven results

Meep-Meep

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On my own car, the 69 RR with a 426MW short block, 915 heads and an OEM iron 6BBL setup, I have logged about 10,000 miles so far and not so much have turned a screw once I sorted out the center carb. For anyone interested, my combo is mild but it makes very good power for a street car that can be driven daily. Average fuel economy is 13 MPG tested with a speedometer head that has been calibrated with correct gear used. I bet it can pull 16 MPG on a flat steady cruise. For those who have a mild build and think 8 MPG is normal (not driving at WOT all the time) need to keep reading. You are likely damaging your engine by washing the rings. The extra fuel over time dilutes the oil and will drastically shorten the life of the block, rings and pistons. This is true for any engine.

The engine is as stated, a 62 413 MW bored to .030" 426. Why? Because I had it lying around and have a long history with this very block dating back to my street racing days in the 80s. Right now I'm running a set of (good swap meet deal) Ross pistons that I cut down to zero deck flat tops. Compression is CC'd at 9.5:1. The cam is a MoPar .455 / 272. Timing at 12 I with about 35 total all in by 2500-ish. Hooker 2" headers. 4 speed with 3.23 gears. 3" TTI H pipe into Accurate 2.5" tails with 20" Thrush Hush mufflers. Car weighs 3970 with me in it. Call it 4000 lbs.

When this first got running I noticed on the O2 sensor that it was very rich at tip in. Also the outboard carbs came in way too soon. The rich condition was puzzling because I could get the idle to 14.5:1 but at tip in I would see 10.5-11:1. Even at cruise (3.55 gears at the time) it would be 11.5:1. The first step was to disconnect the outboard carbs and run on the center. I did this for about 2 months. WOT AFR was damn near perfect at 12.5:1 on the center carb. PV is a 5.5 based on my idle vacuum of 12" HG. After some thinking I came to the conclusion that the idle feed restriction was to big causing the rich condition on tip in and cruise. Not main jets. Those remain stock. So I got a QF metering block, and after a few tries, I settled on a .025 IFR with OEM sized air bleeds. While I had the carb off I took the opportunity to drill and tap for replaceable air bleeds. The result is a very consistent AFR between 14 and 14.5:1 from idle all the way to freeway cruise. There is a noticeable flat spot just at the clutch friction point depending on how hard you leave. This is due to the leaner IFR but expected to be covered up with a different pump cam. Using the white 218 cam now and stock squirter so I think there is a little room for improvement.

Once the center carb was happy I began to look at the outboards. WOT was and still is a tad lean depending on the weather but seems to run OK. Though I might get a bit more power going from 13:1 to 12.5:1. The main issue with the outboards was they were opening too quickly because there is no check ball in the diaphragm body to meter / delay the signal. The new repo cabs do not come with this ball nor is the ball seat configured to accept it. The true OEM ball seat has four very fine grooves that create a small leak around the ball to meter the air flow. I can't over emphasize how important it is to delay the signal to the carbs using a factory intake. And everyone who thinks the yellow spring must be used because that's what the DC manual says is missing a very important point. I have the plain OEM springs and it's perfect. Even the black spring can't delay the opening without the check ball but it will prevent the outboards from opening all the way. These are observations I made watching this setup on a chassis dyno. For those who think vacuum secondaries don't open fast enouigh need to stick their head in the air cleaner and watch. Spoiler alert. The opening rate is not linear. It's nearly instant to about 1/2 throttle with no ball.

Track performance on street tires in complete street trim is low 14 sec 1/4 mile (yes that sucks). But street radials, 3.23s with a 4 speed with an engine that has incredibly good response is not a recipe for a hard launch. Plus I'm out of practice in peddling out of the hole. Used to do much better. However, the MPH is 105. It pulls hard all the way to the point my clutch no longer holds shifting from 3rd to 4th right at the end. That cost me some MPH and a little ET. With slicks, gears and a clutch that holds, this is a high 12 second car through the restrictive and quiet mufflers.

I hope the above provides some useful information and answers some questions that many have about the 6BBL set up. While my setup still has a few areas that need work, its a long way from what it was. The simple center carb mod solved 95% of my drivability issues.
 
I believe it takes more like twice the 413's .030 overbore
to reach 426 Displacement.

Great Post!
 
I read it as the bore size is now a .030 over 426. Which is 4.280, and .100 over the 413 bore.

yes good reading, thanks.
 
On my own car, the 69 RR with a 426MW short block, 915 heads and an OEM iron 6BBL setup, I have logged about 10,000 miles so far and not so much have turned a screw once I sorted out the center carb. For anyone interested, my combo is mild but it makes very good power for a street car that can be driven daily. Average fuel economy is 13 MPG tested with a speedometer head that has been calibrated with correct gear used. I bet it can pull 16 MPG on a flat steady cruise. For those who have a mild build and think 8 MPG is normal (not driving at WOT all the time) need to keep reading. You are likely damaging your engine by washing the rings. The extra fuel over time dilutes the oil and will drastically shorten the life of the block, rings and pistons. This is true for any engine.

The engine is as stated, a 62 413 MW bored to .030" 426. Why? Because I had it lying around and have a long history with this very block dating back to my street racing days in the 80s. Right now I'm running a set of (good swap meet deal) Ross pistons that I cut down to zero deck flat tops. Compression is CC'd at 9.5:1. The cam is a MoPar .455 / 272. Timing at 12 I with about 35 total all in by 2500-ish. Hooker 2" headers. 4 speed with 3.23 gears. 3" TTI H pipe into Accurate 2.5" tails with 20" Thrush Hush mufflers. Car weighs 3970 with me in it. Call it 4000 lbs.

When this first got running I noticed on the O2 sensor that it was very rich at tip in. Also the outboard carbs came in way too soon. The rich condition was puzzling because I could get the idle to 14.5:1 but at tip in I would see 10.5-11:1. Even at cruise (3.55 gears at the time) it would be 11.5:1. The first step was to disconnect the outboard carbs and run on the center. I did this for about 2 months. WOT AFR was damn near perfect at 12.5:1 on the center carb. PV is a 5.5 based on my idle vacuum of 12" HG. After some thinking I came to the conclusion that the idle feed restriction was to big causing the rich condition on tip in and cruise. Not main jets. Those remain stock. So I got a QF metering block, and after a few tries, I settled on a .025 IFR with OEM sized air bleeds. While I had the carb off I took the opportunity to drill and tap for replaceable air bleeds. The result is a very consistent AFR between 14 and 14.5:1 from idle all the way to freeway cruise. There is a noticeable flat spot just at the clutch friction point depending on how hard you leave. This is due to the leaner IFR but expected to be covered up with a different pump cam. Using the white 218 cam now and stock squirter so I think there is a little room for improvement.

Once the center carb was happy I began to look at the outboards. WOT was and still is a tad lean depending on the weather but seems to run OK. Though I might get a bit more power going from 13:1 to 12.5:1. The main issue with the outboards was they were opening too quickly because there is no check ball in the diaphragm body to meter / delay the signal. The new repo cabs do not come with this ball nor is the ball seat configured to accept it. The true OEM ball seat has four very fine grooves that create a small leak around the ball to meter the air flow. I can't over emphasize how important it is to delay the signal to the carbs using a factory intake. And everyone who thinks the yellow spring must be used because that's what the DC manual says is missing a very important point. I have the plain OEM springs and it's perfect. Even the black spring can't delay the opening without the check ball but it will prevent the outboards from opening all the way. These are observations I made watching this setup on a chassis dyno. For those who think vacuum secondaries don't open fast enouigh need to stick their head in the air cleaner and watch. Spoiler alert. The opening rate is not linear. It's nearly instant to about 1/2 throttle with no ball.

Track performance on street tires in complete street trim is low 14 sec 1/4 mile (yes that sucks). But street radials, 3.23s with a 4 speed with an engine that has incredibly good response is not a recipe for a hard launch. Plus I'm out of practice in peddling out of the hole. Used to do much better. However, the MPH is 105. It pulls hard all the way to the point my clutch no longer holds shifting from 3rd to 4th right at the end. That cost me some MPH and a little ET. With slicks, gears and a clutch that holds, this is a high 12 second car through the restrictive and quiet mufflers.

I hope the above provides some useful information and answers some questions that many have about the 6BBL set up. While my setup still has a few areas that need work, its a long way from what it was. The simple center carb mod solved 95% of my drivability issues.

Thanks for posting.

Here is mine.
440 - 6 Pack
Heavy TRW pistons, no quench
Same cam - 272/.455"
Same heads - 915s, standard size valves, but ported
67 Charger - 4200 lb race weight
Hp exhaust manifolds
2 1/4" exhaust
3.23 gear
factory stock 12" torque converter
P 235-70-14 BFG tires

No O2 sensor, no fancy metering blocks. Just old fashoned tuning.
12-13 mpg. Never more than 14, never less than 11. But this car was WOT a lot.

With the BFGs, ran a best of 12.85 @ 109. 12.90s were typical at 107 plus.

Anything stiffer than the yellow spring slowed the car down. Even reducing the kill bleed size picked the car up.
 
Where is this check ball located that you mention for the end carbs, diaphragm.?
There are no check balls that I am aware of in mine.
 
Where is this check ball located that you mention for the end carbs, diaphragm.?
There are no check balls that I am aware of in mine.

Same here. No check balls. My carbs are from 1969.
 
So about the 413. It's a 62 dated block and was a STD 426 when I got it in the 80s. Someone must have bored it before I got it. All I did was clean it up at .030".
 
Where is this check ball located that you mention for the end carbs, diaphragm.?
There are no check balls that I am aware of in mine.
On all Holleys that I have seen the ball is under the diaphragm lid. Follow the vacuum passage from the side and it ends up going to the lid.
 
Thanks for posting.

Here is mine.
440 - 6 Pack
Heavy TRW pistons, no quench
Same cam - 272/.455"
Same heads - 915s, standard size valves, but ported
67 Charger - 4200 lb race weight
Hp exhaust manifolds
2 1/4" exhaust
3.23 gear
factory stock 12" torque converter
P 235-70-14 BFG tires

No O2 sensor, no fancy metering blocks. Just old fashoned tuning.
12-13 mpg. Never more than 14, never less than 11. But this car was WOT a lot.

With the BFGs, ran a best of 12.85 @ 109. 12.90s were typical at 107 plus.

Anything stiffer than the yellow spring slowed the car down. Even reducing the kill bleed size picked the car up.
My example before this build was a 440 with the same cam and heads. 10:1 CR. Hooker big tube headers. Auto with 4.10s and slicks. 4000 lb as raced (66 Belvy). 12.80 @ 109 but with a factory 4BBL intake and a 750 AFB. When I tried the 6BBL it was an abysmal failure but that was before I figured out the check balls. As of now I can't get below low 14s but the MPH is up there. Just spins the tires.
 
I purchased my carbs new. I don’t remember removing any check balls, but that was a long time ago. It does look like there is a ball seat with the grooves. Certainly there aren’t any check balls now.

Anyways, no check balls, yellow spring, kill bleeds at either 0.038, or 0.035. This produced the best et & mph.

What is the kill bleed size on yours?

IMG_2258.jpeg


IMG_2259.jpeg


IMG_2261.jpeg


IMG_2262.jpeg
 
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I purchased my carbs new. I don’t remember removing any check balls, but that was a long time ago. It does look like there is a ball seat with the grooves. Certainly there aren’t any check balls now.

Anyways, no check balls, yellow spring, kill bleeds at either 0.038, or 0.035. This produced the best et & mph.

What is the kill bleed size on yours?

View attachment 1581307

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View attachment 1581310
Thanks for the info. Interesting you have the yellow spring and it seems to work. Kill bleeds as in high speed bleeds? I don't recall but I drilled and tapped the center carb for replaceable bleeds just in case but matched the size of the originals. On the outboard carbs the vacuum has the bleed off port and my carbs were different. Ended up drilling the smaller to the same size as the larger. Again, I don't recall but maybe about .062" hole.

On the subject of jetting, if you find yourself having to go way up on the outboards it may be a sign that they are opening too quickly. Then of course going too rich after things catch up - assuming you have enough road to make the test! There isn't a transition to cover the instant slam of air so opening too early tends to create the classic bog until the RPM goes up and suficient pressure drop can move fuel. In my case, delaying the opening with the check balls helped immensely. I have the QF jet plate and running something like 85s and they are a tad lean depending on the air. I'm going to bring them up two sizes and see what that does. Shooting for 12.5:1 AFR on the big end. Relying on the center carb until things really get going has proven extremely effective. Ask the guy in the 2000 LS powered Firebird who wanted to play. From a 30 MPH roll he simply disappeared from view and the outboards only came on a split second after I got rolling. Something to be said for the instant responce on the 350 2BBL on the big engine. Center carb has the stock 62 jets. Or is it 63? Whatever the case they are what was in there and it runs 12.5:1 by itself WOT.
 
Still a mystery to me, these check balls in the diaphragm. So I walked out to the garage and got my Holley 2300 parts sheet blow up, I see no check ball in the diaphragm. ????
 
Still a mystery to me, these check balls in the diaphragm. So I walked out to the garage and got my Holley 2300 parts sheet blow up, I see no check ball in the diaphragm. ????
The diaphragm may or may not have the grooved seat. I have seen some replacement carbs with no grooves so I'm not exactly sure what's going on. Putting the check balls in my carbs made all the difference in terms of a favorable opening rate (delay). It's also common for the outboards to hang open for a bit after you let off the throttle. Some say this is because of the check ball but reality says they will want to hang open no matter what. Decades ago, on these same carbs (no check balls then) and when my buddy owned them, a mechanic friend of his suspected the safety linkage was causing the carbs to bind and not open so he took it off. We went for a ride and the throttle stuck wide open with no way to shut it down other than kill the ignition, which the mechanic did.
 
Thanks for posting the link. I didn’t read it all in detail, but it looks like the conclusion was no check balls?

Me, Lew (one of the posters in the 2015 thread above), and two other guys Jim and Steve, spent years together doing track testing on our street 440 cars with the Six Pack. Lew, with his very mild 9.2:1 CR, 3.23, 12” converter, exhaust manifold car on BFG tires was running 13.0s at 107-108 mph, if memory serves me right. He was testing several stock-ish cams at the time, including the MP 0.455”. I don’t recall if he was using that cam when he was running the 13.0s, or the Hughes 2330 or Comp, 270 Magnum. Like I said, we did a lot of testing. Jim and Steve at the time were on our heels, low 13s @ 104-105 with small hydraulic cams, full street trim and exhaust. Jim’s car, after a rebuild, was nearly identical to your car with small tube headers, 9.5:CR and 4-speed. He did install the MP 528 solid. It was running 12.70 at 112 mph. These cars ran well despite us all having crappy 60 ft time of 2.0 or slower.

Personally, I’ve been playing with my Six Packs since 1977, on everything from mild 383 to roller cam 500 inch motors, all in street cars. This includes engine dynos, chassis dynos, and a lot passes at the track over several years in my 440 Charger.

Anyways, here are my high level take aways:

1) The original, unaltered Six Pack works pretty well on just about everything without modifications. Minor mods will help a little. The jetting is pretty close for everything from a stock motor to 11 second street cars.

2) The best track performance for outboard carb opening rate is a function of the car and can only be determined at the track. The same motor might need the black spring in one car, but the yellow spring in a different car.

3) For a typical street car, if you slow the carb opening rate in an attempt to eliminate the sag (lean spike) during street WOT, you may have slowed the car down in et and mph track performance, and it can be a lot - 0.3 sec and 3 mph. Again, it is a function of the car.

Regarding outboard springs, note Lew’s comment about his car slowing from using stiffer springs than the yellow spring.

Couple Pics of the guys, back when cameras had stuff called film.

Sorry if I'm hijacking your thread, I guess that this thread made me a bit nostalgic.

Jim 1.jpg


Lou 1 crop 2.jpg


Steve Challanger 1.jpg


Russ 02 cropped.jpg
 
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Thanks for posting the link. I didn’t read it all in detail, but it looks like the conclusion was no check balls?

Me, Lew (one of the posters in the 2015 thread above), and two other guys Jim and Steve, spent years together doing track testing on our street 440 cars with the Six Pack. Lew, with his very mild 9.2:1 CR, 3.23, 12” converter, exhaust manifold car on BFG tires was running 13.0s at 107-108 mph, if memory serves me right. He was testing several stock-ish cams at the time, including the MP 0.455”. I don’t recall if he was using that cam when he was running the 13.0s, or the Hughes 2330 or Comp, 270 Magnum. Like I said, we did a lot of testing. Jim and Steve at the time were on our heels, low 13s @ 104-105 with small hydraulic cams, full street trim and exhaust. Jim’s car, after a rebuild, was nearly identical to your car with small tube headers, 9.5:CR and 4-speed. He did install the MP 528 solid. It was running 12.70 at 112 mph. These cars ran well despite us all having crappy 60 ft time of 2.0 or slower.

Personally, I’ve been playing with my Six Packs since 1977, on everything from mild 383 to roller cam 500 inch motors, all in street cars. This includes engine dynos, chassis dynos, and a lot passes at the track over several years in my 440 Charger.

Anyways, here are my high level take aways:

1) The original, unaltered Six Pack works pretty well on just about everything without modifications. Minor mods will help a little. The jetting is pretty close for everything from a stock motor to 11 second street cars.

2) The best track performance for outboard carb opening rate is a function of the car and can only be determined at the track. The same motor might need the black spring in one car, but the yellow spring in a different car.

3) For a typical street car, if you slow the carb opening rate in an attempt to eliminate the sag (lean spike) during street WOT, you may have slowed the car down in et and mph track performance, and it can be a lot - 0.3 sec and 3 mph. Again, it is a function of the car.

Regarding outboard springs, note Lew’s comment about his car slowing from using stiffer springs than the yellow spring.

Couple Pics of the guys, back when cameras had stuff called film.

Sorry if I'm hijacking your thread, I guess that this thread made me a bit nostalgic.

View attachment 1582228

View attachment 1582229

View attachment 1582230

View attachment 1582231
Not hijacking at all. In fact, I say this is a discussion as intended to be.

For me the 6BBL is relatively new and all I'm doing is collecting data and making corrections based on the data. So far I'm doing well. Regarding the track performance vs. street, I couldn't agree more. When my set up wan on a 440 (with same cam) it ran OK on the street. At the track it literally laid down just past the tree. It was like hitting the brakes. Same car with a 4BBL was 12.80 @ 109 with a factory iron intake. Later I put that 6BBL on a dyno and was amazed at how fast those carbs opened but only to about half throttle. The check balls may not have been factory but the goal is to delay and slow the opening. In may case taking them out results in more noise (ba-wooo) but not much forward motion. Comparing street performance delaying and slowing the opening produces really good results. Agreed, I should do some back to back track testing but right now my clutch won't take another round. The 3.23s don't help the situation either. Once I put my Passon OD 4 speed back in with the 3.70s then I can play more. But I'm still impressed with the MPH running the 3.23 and full Thrush Hush mufflers out the back.
 
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